a) Field of the Invention
This invention relates to ion-selective polymeric membranes for use in electrochemical sensors such as ion-selective electrodes, coated wire electrodes or ion-selective field effect transistors, with applications in analytical chemistry, particularly in clinical and environmental chemistry.
Such devices are electrochemical sensors that allow potentiometric determination of the activity of certain ions in the presence of other ions; the sample under test is usually an aqueous solution. Such a device constitutes a galvanic half-cell, consisting of an ion-selective membrane, an internal contacting solution (optional), and an internal reference electrode. The other half cell is given by an external reference electrode dipping into a reference electrolyte.
In the ideal case, the ion-selective membrane should be permeable only to the analyte ion but non-permeable to all other ions including the analyte counterion. One of the families of membranes under investigation is that in which the membranes contain neutral molecular carriers, namely uncharged lipophilic molecules. These molecules are capable of selectively transporting the analyte ion across a hydrophobic membrane (see "Design features of ionophores for ion selective electrodes", Pretsch et. al., Pure & Appl. Chem., Vol. 60, No. 4 pp567-574, 1988).
b) Description of the Related Art
Use of crown ether compounds in ion-selective electrodes has been proposed (see U.S. Pat. Nos. 4,531,007 Toke et. al: 4,544,362 Shono et. al; and 4,523,994 Shono et. al).
Investigations have also been carried out into the use of calixarene-based ionophores.
Diamond et. al., Analytica Chimica Acta, 204 (1988) 223-231 described a sodium-selective electrode based on the ligand methyl p-t-butylcalix(4)arene acetate. Solutions of this ionophore produced sodium-selective electrodes both in the form of single liquid membranes and when incorporated into PVC membranes. Exchanger anions (TClPB) were included to reduce membrane resistance and to obtain the desired Na.sup.+ selectivity. It was reported that ethyl p-t-butylcalix(4)arene acetate, ethyl p-t-butylcalix(6)arene acetate and ethyl calix(6)arene acetate had produced working liquid membrane electrodes, with the tetramer being Na.sup.+ selective and the hexamers being caesium-selective. However no experimental results were reported for electrodes made with these ligands.
Arnaud-Neu et. al., J. Am. Chem. Soc. 1989, 111, 8681-8691 described ionophoric activity of a group of alkyl calixaryl esters and ketones. Stability constants were determined for the alkali-metal cation complexes of the tetrameric ethyl acetate, the hexameric ethyl acetate, the tetrameric methyl ketone, the tetrameric tert- butyl ketone and the tetrameric phenyl ketone, all being p-tert.-butyl derivatives. However, this publication provided no further teaching about ion-selective electrodes and merely reported the work of Diamond et. al., Anal. Chim. Acta. 1988, 204, 223 mentioned above.
Kimura et. al., Chem. Lett. 1988, 615 described PVC-based membrane electrodes based on decyl p-t-butylcalix(4)arene acetate and p-t-butylcalix(4)arene dibutylamide.
Japanese Patent Publication JP 01,250,750 (89,250,750) Shono et. al., in CA Selects: Synthetic Macrocyclic Compounds, Issue 15, 1990. page 9, Item 113:17168k described a sodium ion-selective membrane electrode containing as a neutral carrier at least one compound of the formula III ##STR3## where R.sup.a =alkyl, allyl
R.sup.b =CH.sub.2 COOR.sup.c, CH.sub.2 CONR.sub.2.sup.c PA1 R.sup.c =hydrophobic hydrocarbon having 4 or more carbon atoms. PA1 m=0-8; PA1 n=0-8; PA1 a, which may be the same or different on each aryl group, is 0 or 1; PA1 R.sup.2 is alkyl aryl, alkaryl, alkoxy, alkoxyalkoxy, aryloxy, alkaryloxy, alicyclic, alkylthio, arylthio, alkarylthio, or a substituted derivative thereof; PA1 R.sup.3 is --H, alkyl or alkenyl; PA1 X is --OH or a group containing an acrylate or methacrylate functional group; PA1 provided that when X is --OH, n is at least 1/2 (n+m); PA1 and provided that when m=0, n=4, a=0 and R.sup.3 is alkyl or allyl, R.sup.2 is not alkoxy having 4 or more carbon atoms in the alkyl group; PA1 and provided that when m=0, n=4, a=0 and R.sup.3 is t-butyl, R.sup.2 is not methoxy or ethoxy;
An ionophore suitable for an ion-selective electrode should have the following properties:
1. Polar groups capable of replacing the hydration shell of the ion that it will complex; PA0 2. High solubility in non-polar solvents and it must be insoluble in water; PA0 3. A cavity of optimum diameter to hold the target ion; PA0 4. The complex formed should remain in the membrane phase; PA0 5. Complex formation which is fast and reversible. PA0 a) a supporting matrix, and PA0 b) an ionophore selected from calixarene or oxacalixarene derivatives of the formula IV ##STR4## wherein n+m=3-8; PA0 n'=1-5, preferably 2 PA0 m'=1-5, preferably 1, 2 or 4 PA0 n"=0 or 1, preferably 1. PA0 R" is H or CH.sub.3.